Catalytic converter

Abstract

The problem that the technology disclosed herein aims to solve is to suppress the decrease in reaction efficiency due to endothermic reactions in a catalytic device that generates a reaction gas from a raw material gas using a chemical reaction involving an endothermic reaction. [Solution] The catalyst device 1, which chemically reacts a raw material gas with a reaction gas, has a flow path 3, a catalyst 10 placed in the flow path 3, and a flow velocity reducing member 12 placed in the flow path 3. The raw material gas generates a reaction gas through a chemical reaction involving an endothermic reaction. The temperature inside the flow path 3 decreases due to the endothermic reaction. The flow velocity reducing member 12 shrinks due to the decrease in temperature.

Description

Technical Field

[0001] The present invention relates to a catalytic apparatus for chemically reacting a raw material gas into a reaction gas.

Background Art

[0002] Patent Document 1 discloses a catalyst structure that decomposes ammonia in a raw material gas to produce hydrogen in a reaction gas. Metal fine particles are used as a catalyst for decomposing ammonia. The catalyst structure is constituted by supporting the catalyst inside a porous carrier of a zeolite-type compound. The chemical reaction for decomposing ammonia into hydrogen and nitrogen is an endothermic reaction. The decomposition efficiency decreases due to heat absorption as ammonia is decomposed. In order to maintain the decomposition efficiency in the conventionally provided catalyst structures and catalytic apparatuses, it is necessary to heat the catalyst and moreover, it is necessary to control the heating. Therefore, there has been room for improvement in catalytic apparatuses using chemical reactions involving endothermic reactions.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The problem to be solved by the technology disclosed in this specification is to suppress the decrease in reaction efficiency due to heat absorption in a catalytic apparatus that generates a reaction gas from a raw material gas using a chemical reaction involving an endothermic reaction.

Means for Solving the Problems

[0005] According to one feature of this disclosure, a catalytic device for chemically reacting a raw material gas with a reaction gas comprises a flow channel, a catalyst placed in the flow channel, and a flow velocity reducing member placed in the flow channel. The raw material gas generates a reaction gas through a chemical reaction involving an endothermic reaction. The temperature inside the flow channel decreases due to the endothermic reaction. The flow velocity reducing member shrinks due to the decrease in temperature.

[0006] Therefore, heating the catalyst also heats the velocity-reducing member placed in the same flow path. This causes the velocity-reducing member to expand due to heat. As the temperature in the flow path decreases due to the endothermic reaction, the velocity-reducing member contracts from its expanded state. The voids in the flow path expand as the velocity-reducing member contracts due to heat. As the voids in the flow path expand, the flow velocity of the raw material gas decreases, and the time the raw material gas is in contact with the catalyst increases. This can increase the reaction efficiency of the chemical reaction. Thus, by expanding the voids in the flow path, the decrease in the reaction efficiency of the chemical reaction due to endothermic heat can be suppressed.

[0007] According to other features of this disclosure, the velocity-reducing member has a greater coefficient of thermal expansion than the catalyst. Therefore, when the velocity-reducing member contracts due to heat, it can efficiently expand the voids in the flow path. This makes it possible to more reliably suppress the decrease in the reaction efficiency of the chemical reaction due to endothermic factors.

[0008] According to other features of this disclosure, the velocity-reducing member is granular or lumpy. Therefore, the velocity-reducing member can be easily placed in the gaps between catalysts. This allows the gaps that expand when the velocity-reducing member shrinks due to heat to be adjacent to the catalysts. As a result, the reaction efficiency of the chemical reaction can be efficiently increased by expanding the gaps in the flow path.

[0009] According to other features of this disclosure, the velocity-reducing member is made of stainless steel or aluminum. Therefore, the velocity-reducing member can be made of a material that has a high coefficient of thermal expansion and low reactivity with the source gas and reaction gas, making it suitable as a catalyst.

[0010] According to other features of this disclosure, the raw material gas is ammonia and the flow velocity reducing member is stainless steel. Therefore, the flow velocity reducing member can be made of a material with a high coefficient of thermal expansion and low reactivity with ammonia, hydrogen, and nitrogen. [Brief explanation of the drawing]

[0011] [Figure 1] This is a block diagram of a fuel cell system equipped with a catalyst device related to this disclosure. [Figure 2] This is a longitudinal cross-sectional view schematically showing a catalyst device according to the first embodiment. [Figure 3] This is a schematic longitudinal cross-sectional view showing the catalyst layer when the temperature rises. [Figure 4] This is a longitudinal cross-sectional view schematically showing the catalyst layer when the temperature decreases. [Modes for carrying out the invention]

[0012] Hereinafter, a first embodiment of the catalyst device of this disclosure will be described with reference to Figures 1 to 4. The same reference numerals in the description refer to the same elements having the same function, without requiring redundant explanation. As shown in Figure 1, the catalyst device 1 is provided in a fuel cell system 20. The fuel cell system 20 has an ammonia storage unit 21 upstream of the catalyst device 1. The fuel cell system 20 has an adsorption unit 22 downstream of the catalyst device 1, and a fuel cell (FC) 23 is located further downstream.

[0013] As shown in Figure 1, ammonia (NH3) is introduced from the ammonia storage unit 21 to the catalyst unit 1 as a raw material gas. In the catalyst unit 1, the ammonia is decomposed into hydrogen (H2) and nitrogen (N2), producing a reaction gas containing hydrogen and nitrogen. The reaction gas and a mixed gas containing trace amounts of undecomposed ammonia are discharged from the catalyst unit 1 to the adsorption unit 22. The adsorption unit 22 adsorbs the ammonia contained in the mixed gas. The purified gas, from which ammonia has been removed from the mixed gas, is introduced to the fuel cell 23. The fuel cell 23 generates electricity using the hydrogen contained in the purified gas as fuel.

[0014] As shown in Figure 2, the catalyst device 1 has a substantially cylindrical housing 2. A flow path 3 is provided inside the housing 2. At the upstream end of the housing 2, a raw material gas inlet 3a is provided, which communicates with the flow path 3. Ammonia, the raw material gas, is introduced into the flow path 3 of the catalyst device 1 from the upstream ammonia storage unit 21 (see Figure 1) via the raw material gas inlet 3a. At the downstream end of the housing 2, a reaction gas outlet 3b is provided, which communicates with the flow path 3. The reaction gas, a mixed gas containing hydrogen and nitrogen, is discharged from the flow path 3 to the downstream adsorption device 22 (see Figure 1) via the reaction gas outlet 3b.

[0015] As shown in Figure 2, the majority of the flow path 3 is a catalyst layer 5 with a substantially constant cross-sectional area perpendicular to the flow direction. The cross-sectional area of ​​the catalyst layer 5 is substantially constant from the inlet 5a at the upstream end to the outlet 5b at the downstream end. A heater 4 is provided on the radially outer side of the housing 2. The heater 4 heats the catalyst layer 5 substantially uniformly. The radial outer circumference of the heater 4 is covered with an insulating material (not shown).

[0016] As shown in Figure 2, the catalyst layer 5 contains a plurality of catalysts 10 and a plurality of velocity-reducing members 12. The catalysts 10 are in the form of approximately spherical granules or lumps. The velocity-reducing members 12 are in the form of granules or lumps, such as approximately spherical, columnar, rod-shaped, or plate-shaped. In this disclosure, a substantially cylindrical velocity-reducing member 12 is given as an example. The plurality of catalysts 10 and the plurality of velocity-reducing members 12 are mixed fairly uniformly within the catalyst layer 5. Gaps 11 are formed between the plurality of catalysts 10, between the plurality of velocity-reducing members 12, or between the catalysts 10 and the velocity-reducing members 12. As shown in Figure 3, the plurality of catalysts 10 have an average particle size 10a and are provided in substantially the same size and shape. The average expansion length 10a of the plurality of velocity-reducing members 12 is the average of the maximum lengths that expand when heated by a heater. The plurality of velocity-reducing members 12 are provided in substantially the same size and shape. The size, number, and packing density of the catalyst 10 and flow velocity reducing members 12 shown in the figure are approximate for illustrative purposes only and do not specify concrete values. Therefore, for example, the size ratio of the catalyst 10 and flow velocity reducing members 12 to the housing 2 is not specified, nor is the mixing ratio of multiple catalysts 10 and multiple flow velocity reducing members 12 specifically determined.

[0017] As shown in FIGS. 2 and 3, the catalyst 10 is formed by mixing and baking metal fine particles or the like that function as the catalyst itself with a carrier. Metal fine particles or the like are supported on the surface of the catalyst 10. The material of the metal fine particles or the like may be at least one of, for example, ruthenium, nickel, cobalt, and palladium, but is not limited thereto and may be other metals, alloys, or the like.

[0018] As shown in FIGS. 2 and 3, the flow rate reducing member 12 is formed of a material having a large coefficient of thermal expansion (linear expansion coefficient). The material of the flow rate reducing member 12 is more preferably a material having low reactivity with ammonia of the raw material gas and hydrogen and nitrogen of the reaction gas and being difficult to corrode. The material of the flow rate reducing member 12 is, for example, stainless steel (SUS) having a linear expansion coefficient of 18 [×10 -6 / K] or aluminum having 26 [×10 -6 / K], and more preferably stainless steel. The material of the flow rate reducing member 12 may be a material having a linear expansion coefficient equal to or greater than that of stainless steel, and may be, for example, a metal material such as magnesium and zinc, or an alloy such as brass and duralumin.

[0019] As shown in FIG. 3, the flow rate reducing member 12 expands to an average length in the longitudinal direction of the average expansion length 12a by being heated by the heater 4 (see FIG. 2). When the flow rate reducing member 12 is made of stainless steel, the volume increase amount per 1 cm 3 when the temperature rises by 100 ° C. is approximately 5.4 mm 3 . When the flow rate reducing member 12 is made of aluminum, the volume increase amount per 1 cm 3 when the temperature rises by 100 ° C. is approximately 7.8 mm 3 . On the other hand, the coefficient of thermal expansion of the catalyst 10 is a sufficiently small positive value or negative value with respect to the flow rate reducing member 12. For example, the linear expansion coefficient of the catalyst 10 is 20% or less, 10% or less, 5% or less of the flow rate reducing member 12. Therefore, the catalyst 10 has a very small volume increase amount with respect to the temperature rise, or slightly contracts as the temperature rises. Therefore, the average particle diameter 10a of the catalyst 10 is substantially constant when not heated, when heated, and when the temperature drops due to the endothermic reaction described later.

[0020] As shown in FIG. 3, when the flow rate reducing member 12 thermally expands due to heating by the heater 4 (see FIG. 2), the gap 11 around the flow rate reducing member 12 becomes narrower by the volume of the thermal expansion. On the other hand, the catalyst 10 maintains a substantially constant volume even when heated by the heater 4. Therefore, the reduction of the gap 11 occurs around the flow rate reducing member 12. As the gap 11 around the flow rate reducing member 12 becomes narrower, the flow rate of the gas in the flow path 3 increases. Therefore, the time for the raw material gas to contact the catalyst 10 decreases. Since the efficiency of the chemical reaction is increased by heating the catalyst 10, even if the flow rate of the raw material gas increases and the contact time with the catalyst 10 decreases, the raw material gas can be sufficiently chemically reacted to produce the reaction gas.

[0021] The chemical reaction for decomposing ammonia into hydrogen and nitrogen involves an endothermic reaction. Therefore, as shown in FIG. 4, as ammonia is decomposed, heat in the flow path 3 is absorbed by the endothermic reaction. Therefore, the temperature in the flow path 3 decreases compared to the start of heating by the heater 4 (see FIG. 2). The flow rate reducing member 12 thermally contracts until the average length in the longitudinal direction becomes the average contraction length 12b. The gap 11 around the flow rate reducing member 12 expands by the volume of the thermal contraction. On the other hand, the catalyst 10 maintains a substantially constant volume even when the temperature decreases due to the endothermic reaction. Therefore, the increase in the gap 11 occurs around the flow rate reducing member 12.

[0022] As shown in FIG. 4, as the gap 11 around the flow rate reducing member 12 expands, the flow rate of the gas in the flow path 3 decreases. Therefore, the time for the raw material gas to contact the catalyst 10 increases. By reducing the flow rate of the raw material gas and increasing the contact time with the catalyst 10, a decrease in the reaction efficiency due to a temperature decrease can be suppressed. Thereby, the raw material gas can be sufficiently chemically reacted, and the production efficiency of the reaction gas can be maintained.

[0023] As described above, the catalyst device 1 for chemically reacting the raw material gas into the reaction gas has a flow path 3, a catalyst 10 disposed in the flow path 3, and a flow rate reducing member 12 disposed in the flow path 3, as shown in FIGS. 2 and 4. The raw material gas generates a reaction gas by a chemical reaction involving an endothermic reaction. The temperature in the flow path 3 decreases due to the endothermic reaction. The flow rate reducing member 12 thermally contracts due to the temperature decrease.

[0024] Therefore, by heating the catalyst 10, the velocity-reducing member 12, which is also located in the same flow path 3, is heated. This causes the velocity-reducing member 12 to expand due to heat. As the temperature in the flow path 3 decreases due to the endothermic reaction, the velocity-reducing member 12 contracts from its expanded state. The void 11 in the flow path 3 expands as the velocity-reducing member 12 contracts due to heat. As the void 11 in the flow path 3 expands, the flow velocity of the raw material gas decreases, and the time the raw material gas is in contact with the catalyst 10 increases. This increases the reaction efficiency of the chemical reaction. Thus, by expanding the void 11 in the flow path 3, the decrease in the reaction efficiency of the chemical reaction due to endothermic heat can be suppressed.

[0025] As shown in Figure 4, the velocity-reducing member 12 has a greater coefficient of thermal expansion than the catalyst 10. Therefore, when the velocity-reducing member 12 contracts due to heat, it can efficiently expand the void 11 in the flow channel 3. This makes it possible to more reliably suppress the decrease in reaction efficiency of the chemical reaction due to endothermic factors.

[0026] As shown in Figures 2-4, the velocity-reducing member 12 is granular or lumpy. Therefore, the velocity-reducing member 12 can be easily placed in the gaps 11 between the catalysts 10. This allows the gaps 11 that expand when the velocity-reducing member 12 thermally contracts to be adjacent to the catalysts 10. As a result, the reaction efficiency of the chemical reaction can be efficiently increased by expanding the gaps 11 in the flow path 3.

[0027] As shown in Figures 2-4, the flow velocity reducing member 12 is made of stainless steel or aluminum. Therefore, the flow velocity reducing member 12 can be made of a material that has a high coefficient of thermal expansion and low reactivity with the raw material gas and reaction gas, making it suitable as a catalyst 10.

[0028] As shown in Figures 2-4, the raw material gas is ammonia, and the flow velocity reducing member 12 is stainless steel. Therefore, the flow velocity reducing member 12 can be made of a material with a high coefficient of thermal expansion and low reactivity with ammonia, hydrogen, and nitrogen.

[0029] The technologies disclosed herein are not limited to the embodiments described above and are subject to various modifications. A catalytic device for decomposing ammonia is provided as an example. However, the technologies are applicable to catalytic devices in general that utilize chemical reactions involving endothermic reactions.

[0030] An example of a catalyst 10 in which metal nanoparticles are mixed with a carrier and the metal nanoparticles are exposed on the surface is shown. Alternatively, for example, metal nanoparticles may be coated onto the surface of the carrier. For example, a metal that functions as the catalyst body may be formed into particles and used as a catalyst. The material, shape, size, etc. of the catalyst 10 are not limited to those shown in the example and may be changed as appropriate. For example, the shape of the catalyst 10 may be non-spherical, or the catalyst 10 may be provided in a non-granular form such as a porous form, and the flow velocity reducing member 12 may be placed inside the catalyst 10. When the catalyst is non-spherical, the "particle size" may be replaced with, for example, the maximum length of the granular catalyst, or the average value of the maximum and minimum lengths.

[0031] The material, shape, size, etc. of the flow velocity reducing member 12 are not limited to those exemplified and may be changed as appropriate. For example, the flow velocity reducing member 12 may be changed to a material with a larger coefficient of linear expansion than the catalyst 10, and a material with low reactivity with the raw material gas and reaction gas is more preferable. For example, a cylindrical flow velocity reducing member 12 is exemplified, but it may be replaced with a roughly spherical, prismatic, rod-shaped, plate-shaped, etc. For example, the flow velocity reducing member 12 may be made into an elongated shape with a long maximum length to increase the amount of thermal contraction in the longitudinal direction when the temperature decreases. For example, it may be provided in a shape and size that allows it to be adjacent to more catalysts 10.

[0032] The ratio of the number of catalysts 10 and the flow rate reducing members 12 within the catalyst layer 5, as well as their volume ratio, may be changed as appropriate. Increasing the proportion of catalysts 10 can improve the efficiency of reaction gas generation. Increasing the proportion of flow rate reducing members 12 can further suppress the decrease in reaction efficiency when the temperature decreases. The distribution of catalysts 10 and flow rate reducing members 12 within the catalyst layer 5 may be uniform, for example. However, the distribution may be biased, for example, by arranging catalysts 10 on the radially outer side of the catalyst layer 5 and flow rate reducing members 12 on the radially inner side of the catalyst layer 5.

[0033] An example configuration has been given in which the catalyst 10 and the flow velocity reducing member 12 are provided separately. Alternatively, for example, the catalyst 10 and the flow velocity reducing member 12 may be provided as a single granular or lump. For example, the catalyst 10 may also serve as the flow velocity reducing member 12. That is, the catalyst 10 and flow velocity reducing member 12 may be made of a material that functions as a catalyst and has a high coefficient of thermal expansion, such as aluminum. [Explanation of Symbols]

[0034] 1…Catalyst device 2… Housing 3…Flow path, 3a…Raw material gas inlet, 3b…Reaction gas outlet 4… Heater 5...Catalyst layer, 5a...Inlet, 5b...Outlet 10...Catalyst, 10a...Average particle size 11...Void 12...Flow velocity reducing member, 12a...Average expansion length, 12b...Average contraction length 20…Fuel cell systems 21…Ammonia storage 22...Adsorption device 23…fuel cell

Claims

1. A catalytic device that chemically reacts a raw material gas with a reaction gas, Flow channels and A catalyst placed in the aforementioned flow path, A catalyst device having a flow velocity reducing member disposed within the flow path, wherein the raw material gas generates the reaction gas through a chemical reaction involving an endothermic reaction, the temperature in the flow path decreases due to the endothermic reaction, and the flow velocity reducing member shrinks due to the decrease in temperature.

2. A catalyst apparatus according to claim 1, The flow velocity reducing member is a catalytic device in which the coefficient of thermal expansion is greater than that of the catalyst.

3. A catalyst apparatus according to claim 2, The aforementioned flow velocity reducing member is a catalyst device in the form of granules or lumps.

4. A catalyst apparatus according to any one of claims 1 to 3, The catalyst device wherein the flow velocity reducing member is made of stainless steel or aluminum.

5. A catalyst apparatus according to claim 4, A catalyst apparatus in which the raw material gas is ammonia and the flow rate reducing member is made of stainless steel.

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